Field of the Invention
The present invention relates to a laminate body in which an atomic layer deposition film is formed on the outer surface of a base material, a gas barrier film formed of the laminate body, and a method of manufacturing the same.
Description of the Related Art
Methods of forming a thin film on the surface of a substance using a gaseous phase that makes a substance move at an atomic/molecular level similar to gas are roughly classified into Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD).
Typical methods of PVD include vacuum deposition, sputtering, and the like. Particularly, with sputtering, a high-quality thin film having excellent uniformity of film quality and film thickness can be formed in general, even though the cost of the apparatus is high. Therefore, this method is being widely applied to display devices such as a liquid crystal display.
CVD is a method of injecting raw material gas into a vacuum chamber and decomposing or reacting one, two, or more kinds of gases on a substrate by means of heat energy to grow a thin solid film. At this time, in order to accelerate the reaction during the film formation or to decrease the reaction temperature, sometimes a plasma or catalyst reaction is concurrently used, and such a method is called Plasma-Enhanced CVD (PECVD) or Cat-CVD respectively. Such CVD features a small degree of film formation defectiveness and is mainly applied to a manufacturing process of semiconductor devices, such as formation of a gate-insulating film.
In recent years, Atomic Layer Deposition (ALD) method has drawn attention. ALD is a method in which a substance adsorbed onto a substrate surface is formed into films layer-by-layer at an atomic level by means of a chemical reaction caused on the surface, and is categorized as a CVD process. A difference between ALD and general CVD is that the so-called CVD (a general CVD) grows thin films by reacting a single gas on a substrate or by simultaneously reacting a plurality of gases on a substrate. On the other hand, ALD is a special film formation method that alternately uses highly-active gas which is called Tri-Methyl Aluminum (TMA) or a precursor and a reactive gas (also called a precursor in ALD) to grow thin films layer-by-layer at an atomic level by means of adsorption caused on the substrate surface and a chemical reaction following the adsorption.
Specifically, a film is formed as follows by ALD. During the surface adsorption caused on the substrate surface, if the surface is covered with a certain type of gas, a so-called self-limiting effect by which the gas is no longer being adsorbed is utilized to discharge unreacted precursors at a point in time when the precursors have been adsorbed onto only one layer. Thereafter, a reactive gas is injected to oxidize or reduce the above precursors and to obtain only one layer of a thin film having a desired composition, and then the reactive gas is discharged. The above treatment is regarded as one cycle, and this cycle is repeated to grow thin films. Accordingly, in an ALD process, thin films grow in a two-dimensional manner. Needless to say, a degree of film formation defectiveness is smaller in the ALD process than in the conventional vacuum deposition, sputtering, and the like than in the general CVD process and the like, and this is the feature of ALD. Consequently, ALD is expected to be widely applied to various fields including the fields of packing foods, pharmaceutical products or electronic parts.
ALD also includes a method that uses plasma for enhancing a reaction in a step of decomposing second precursors and reacting these with a first precursor having been adsorbed onto the substrate. This method is called Plasma-Enhanced ALD (PEALD) or simply called plasma ALD.
The technique of ALD was proposed by Dr. Tuomo Sumtola from Finland in 1974. Generally, since a high-quality and high-density film can be formed by ALD, this method is being increasingly applied to the field of semiconductors such as gate-insulating films, and International Technology Roadmap for Semiconductors (ITRS) also describes this method. Moreover, ALD has a feature in that this method does not provide an oblique shadow effect (a phenomenon in which sputtering particles obliquely enter the substrate surface and thus cause unevenness during film formation) compared to other film formation methods. Accordingly, a film can be formed as long as there is a space into which a gas is injected. Therefore, ALD is expected to be applied not only to coating films of lines and holes on a substrate having a high aspect ratio which indicates a high ratio between the depth and the width, but also to the field relating to Micro Electro Mechanical Systems (MEMS) for coating films of three-dimensional structures.
However, ALD also has faults. That is, for example, special materials are used to perform ALD, and accordingly, the cost increases. However, the biggest fault thereof is the slow film formation speed. For example, the film formation speed thereof is 5 to 10 times slower than that of general film formation methods such as vacuum deposition or sputtering.
As described above, a thin film formed by means of ALD using the above film formation methods can be applied to small plate-like substrates such as wafers or photomasks; inflexible substrates having a large area, such as glass plates; flexible substrates having a large area, such as films; and the like. Regarding equipment for mass-producing such thin films on these substrates according to the use thereof, various substrate-handling methods have been proposed according to the cost, ease of handleability, the quality of formed film, and the like, and have been put to practical use.
For example, a sheet-type film formation apparatus is known that forms a film for a wafer by a sheet of substrate being supplied to the apparatus and then forms a film again on the next substrate replaced, a batch-type film formation apparatus in which a plurality of substrates are set together such that the same film formation processing is performed on all the wafers, or the like.
In addition, regarding an example of forming a film on a glass substrate or the like, an inline-type film formation apparatus is known that forms a film while sequentially transporting substrates to a portion as a source of film formation. Moreover, a coating film formation apparatus is known using a so-called roll-to-roll process in which a substrate, which is mainly a flexible substrate, is wound off and transported from a roller to form a film and the substrate is wound around another roller. This apparatus also includes a web coating film formation apparatus that continuously forms a film by loading not only a flexible substrate but also a substrate on which a film is to be formed on a flexible sheet which can be continuously transported or on a tray of which a portion is flexible.
Regarding the film formation methods or substrate-handling methods used by any of the film formation apparatuses, a combination of the film formation apparatuses that yields the highest film formation speed is employed in consideration of the cost, quality, or ease of handleability.
Moreover, as a related technique, a technique of performing ALD to form a gas permeation barrier layer on a plastic substrate or a glass substrate has been disclosed (for example, see Published Japanese Translation No. 2007-516347 of the PCT International Publication). According to this technique, a light-emitting polymer is loaded on a plastic substrate having flexibility and light permeability, and ALD (top coating) is performed on the surface and the lateral surface of the light-emitting polymer.
As a result, it is possible to reduce coating defectiveness, and a light-permeable barrier film that can substantially reduce a degree of gas permeation in a thickness of tens-of-nanometers can be realized.
As described above, conventionally, laminate bodies in which an atomic layer deposition film is disposed on the outer surface of a base material by means of ALD are known, and these laminate bodies are preferably used for gas barrier films and the like having gas barrier properties. However, the present inventors conducted research and found that in the conventionally known laminate body, an atomic layer deposition film is laminated on a polymeric base material, and the form of growth thereof is highly likely to differ from the form of growth when inorganic crystals such as in the conventional Si wafer are used as a base material. When a substrate obtained by performing oxidation treatment on a Si wafer is used, the density of adsorption sites of the precursors is almost the same as that of the crystal lattice. In many cases, while the atomic layer deposition is being performed by several cycles, after the period of three-dimensional growth (island growth), the film grows in a two-dimensional growth mode. However, it was found that in the case of a polymeric base material, the density of distributed adsorption sites of the precursors is low, the precursors which are adsorbed in a state of being isolated function as nuclei to promote the three-dimensional growth, and an adjacent nucleus comes into contact with the precursors, thereby forming a continuous film. That is, these findings mean that in the growth of the atomic layer into a polymeric base material, the period of three-dimensional growth to form a continuous film is long, the period in which the continuous film becomes a dense film by two-dimensional growth is long, and a dense portion of the atomic layer deposition film that is formed by the two-dimensional growth is decreased. In view of gas barrier properties, the fact that the portion of the two-dimensional growth is small is not preferable. In other words, the conventional laminate body described above may not have ideal gas barrier properties.
Moreover, as described above, since it takes a long time for two-dimensional growth to occur, the portion of the three-dimensional growth that has a low density increases. Accordingly, not only is the binding density lowered, but also the portion of the atomic layer deposition film that has a low mechanical strength increases, whereby the adhesive strength is highly likely to be lowered.
The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a laminate body and a gas barrier film having a high degree of gas barrier properties and a method of manufacturing the laminate body and the gas barrier film.